The present invention is generally directed to a tire monitoring system, and more particularly, to an automotive tire monitoring system.
Historically, automotive tire pressure monitoring (TPM) systems were time-based. That is, a transmitter/sensor located within each tire periodically determined the tire pressure of an associated tire and transmitted the tire pressure along with a unique identification (ID) code, identifying the transmitter, to a receiver located within the vehicle. Typically, a processor, coupled to the receiver, executed a program to determine whether a given transmitter had transmitted within a given time period. When the receiver failed to receive a transmission from the given transmitter during the given time period or periods, the processor typically executed a routine, which removed the ID code associated with the missing transmitter from a main storage array in a memory. In at least one TPM system, an auxiliary storage array was utilized to provide new ID codes to replace those that were associated with the missing transmitter.
An event-based TPM system has executed software such that the system determined, after a number of recognized ID codes were received, whether the transmitter associated with each vehicle tire was still active. The event-based TPM system then attempted to replace ID codes associated with transmitters that failed to transmit for a particular number of events. Event-based TPM systems are normally preferable to time-based TPM systems in that an event-based TPM system can function with a group of transmitters that have different transmission rates from, for example, one group to another group. In a typical event-based TPM system, a processor, connected to an output device, has initiated an audible or visual indication, on the output device, when one of the tires of the vehicle, for example, exhibited a pressure below a low pressure threshold. However, both time-based and event-based TPM systems have required operator inspection or intervention (i.e., training of the systems) to determine the particular location (i.e., front-driver, front-passenger, rear-driver or rear-passenger) of the tire or tires on the vehicle.
Event-based TPM systems, like time-based TPM systems have included a unique ID code for each individual tire transmitter/sensor. Further, each tire transmitter has provided a certain number of data bits (e.g., eight bits representing tire pressure) in each frame (i.e., message). Due to lack of standardization and for functionality reasons, some manufacturers have implemented tire transmitters that have different length ID codes and, in general, different length frames. In addition, while some vehicle manufacturers have included a transmitter/sensor within a spare tire, other vehicle manufacturers have not incorporated a transmitter/sensor within the spare tire.
In some TPM systems, the receiver of the system has been coupled to a data slicer, which has functioned to identify each individual bit of a frame. In the automotive environment, a transmitted message associated with a tire transmitter normally exhibits signal fading due to wheel rotation and may be subject to impulse noise (e.g., high frequency noise attributable to microprocessor switching), which can adversely affect the functioning of the data slicer. As such, some data slicers have used an averaging signal filter to prevent the impulse noise from adversely affecting the data slicer threshold. However, implementing an averaging signal filter in TPM systems that utilize a pulse width modulation (PWM) coding scheme (e.g., thirty-three percent xe2x80x98onxe2x80x99 for a logic zero, and sixty-six percent xe2x80x98onxe2x80x99 for a logic one) is not always desirable. This is because PWM codes have a variable direct current (DC) component, which results in a data slicer threshold that varies depending on the data transmitted. That is, utilizing an averaging signal filter in conjunction with a data slicer typically yields a data slicer threshold that is lower than desired when high levels of impulse noise are present. Further, the averaging signal filter tends to limit the ability of the data slicer threshold to follow variations in the demodulated signal that are attributable to signal fading due to wheel rotation.
Thus, what is needed is a tire monitoring (TM) system that processes data frames of different lengths. Further, it would be desirable for the TM system to function with spare tires that include transmitters as well as spare tires without transmitters. Additionally, it would be desirable for a data slicer associated with the receiver of the TM system to properly function in the presence of impulse noise. Further, it would be desirable for the TM system to automatically associate a received ID code with a particular tire location.
An embodiment of the present invention is directed toward improving the ability of a data slicer, that is coupled to a tire monitoring (TM) system receiver, to properly resolve data bits of a received message in the presence of high noise levels relative to the received message, which also exhibits signal fading. In this embodiment, a peak detector that includes a peak detector input and a peak detector output provides a peak detector signal that corresponds to a peak of a received demodulated signal. The peak detector input is coupled to a first input of the data slicer. A peak detector signal filter is coupled between the peak detector output and a second input of the data slicer and is configured to substantially prevent impulse noise from increasing a variable data slicer threshold on the second input of the data slicer, while simultaneously allowing the data slicer threshold to follow the variations in the demodulated signal attributable to signal fading.
Another embodiment of the present invention is directed toward automatically determining the location of a plurality of vehicle tires relative to a vehicle. A sensor, located in each of the tires, provides an indicator of a rotation direction in a main rotation plane. A transmitter, located within each of the tires, is configured to transmit a unique transmitter identification code and the indicator of the rotation direction in the main rotation plane and another indicator of whether one of the tires has turned out of the main rotation plane to a receiver located in the vehicle.
Yet another embodiment of the present invention is directed to utilizing a single receiver to receive messages of multiple lengths. Initially, a message that includes a plurality of bits, a portion of which correspond to a transmitter identification (ID) code, is received. When a bit is not detected in the received message for a timeout period, a timeout indication is provided. A first indication is provided when the number of bits in the received message is equal to a first number of total bits. A second indication is provided when the number of bits in the received message is equal to a second number of total bits, which is greater than the first number of total bits. The message is then processed according to the first and second indications, which allows different length messages to be distinguished such that the single receiver can receive transmissions from transmitters that have different length messages.
In still another embodiment of the present invention, an alarm, provided by the tire monitoring system, is masked when a transmitter equipped flat tire is replaced with a spare tire that does not include a transmitter. Initially, a transmitter identification code associated with the flat tire is stored. Next, it is determined whether a missing transmitter identification code corresponds to the stored transmitter identification code associated with the flat tire. If so, the alarm is masked.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.